The present invention relates to an ion beam therapy system used in the treatment of cancer and to a method for operating said system according to the preamble independent claims.
Such a therapy system is known for a proton beam from U.S. Pat. No. 4,870,287. The known system is selectively generating and transporting proton beams from a single proton source through an accelerator to selected ones of a plurality of patient treatment stations, each having a rotatable gantry for delivering the proton beam at different angles to patients supported in fixed orientations at the stations.
Especially for heavy ions that means ions heavier than protons a person skilled in the art tries to avoid the application of a rotatable gantry due to the difficulties to rotate heavy and huge equipment. A review about these systems avoiding rotatable gantries for heavy ions is published by E. Pedroni: Beam Delivery, Proc. 1st Int. Symposium on Hadrontherapy, Como, Italy, Oct. 18-21, 1993, page 434. Such systems known by a person skilled in the art need to move the patient in order to reduce either weight or size of rotated equipment. Some designers prefer a set of fixed beam lines instead of a rotating structure like it is known from the paper M. M. Kats, K. K. Onosovski: Instruments and Experimental Techniques Vol. 39, No. 1, 1996, page 1 to 7 and page 1 32. Therefore, it is obvious for a person skilled in the art to design an ion beam therapy system with heavy ions as an excentric system.
Excentric systems have, however, the drawbacks that radiation oncologists do not prefer such solutions since they clearly want and demand an isocentric system.
From the article by Marius Pavlovic in Nuclear Instruments and Methods in Physics Research, Section A, Oct. 11, 1997, Elsevier, vol. 399, no. 2-3, pages 439-454 a gantry design is known for light ions (Z=1-8), comprising superconductive dipoles as bending magnets excluding any edge focusing effects for these superconductive dipoles.
From the article by J. Pawelke et al. in Physics in Medicine and Biology; February 1996; IOP Publishing; Vol. 41, No. 2, pages 279-296 different cameras for in-beam position emission tomograph imaging are known for in situ and in vivo treatment plan verification and beam monitoring as well as dose control during heavy-ion tumor therapy.
From the article by P. Forck et al. in EPAC96, Fifth European Particle Accelerator Conference, Sitges, Spain; Jun. 10-14, 1996, Pages 2644-2646 a scintillator based halo-detector for beam position monitoring is known, used for the cancer therapy. This detector provides informations on the centre-of-mass, the width and the intensity by a sensitive nearly non-destructive method.
It is an object of the present invention to provide an ion beam therapy system and a method for operating the system according to the preamble of independent claims which keep the isocentre fixed with respect to the well defined room coordinate system and which makes the routine patient positioning and checking of the treatment angle easier. Further, the ion beam therapy system should provide a single plane configuration, which requires less bending but leads to a larger gantry length in contrast to the known isocentric xe2x80x9cCork screwxe2x80x9d gantry concept known from A. Koehler: U.S. Pat. No. 4,812,658, Mar. 14, 1989 and S. Z. Rabin et al.: Nucl. Instr. and Meth. B40/41 (1989) page 1335. Therefore it is an aspect of the present invention to reduce also the gantry radius which normally becomes quite large for an isocentric geometry designed for a single plane configuration for ion beams particularly for a heavy ion beam.
Further, it is an aspect of the present invention to avoid the inaccuracy and the uncertainty of an out-beam positron emission tomograph. The positron emission tomograph patient is presently recorded after the irradiation. In this case the patient has to be first transported from the treatment room to the positron emission tomograph. During this time, the original distribution of the positron emitters (mainly 11C and 10C, 13N, 15O) may be significantly deteriorated due to the transport and exchange of matter in the body. This should be avoided with the ion beam therapy system according to the present invention.
Another aspect of the present invention is to monitor the raster scanned ion beam particularly to monitor the raster scanned heavy ion beam after passing the last bending magnet. To measure and control the particle fluence and the beam position with high speed.
The object of the present invention is solved by the features of the subject matter of independent claims. Feature of preferred embodiments are defined with dependent claims.
An advantage of the present invention is that this ion beam therapy system has the possibility of controlling the charged particles by means of magnetic fields. Thanks to that, well focused pencil-like beams of charged particles with an adjustable spot-size can be formed and scanned over the treatment field following Kreisel the tumor contours. By a Variation of the scanning speed and the beam intensity any desired dose distribution within the target volume can be generated with a minimum extra dose delivered to the healthy tissue. The dynamic scanning beam delivery according to the present invention is an ideal technique for 3D-conformal tumor irradiation.
The ion beam therapy system of the present invention has the advantage of a clearly isocentric system with a reduced gantry radius, since the scanning system is located upstream the last bending magnet of the gantry. This position of the scanning system has the additional advantage of a high flexibility of the ion-optical system of the gantry, which can achieve an accurate control of the beam size and dispersion at the isocentre. By means of the edge focussing effect at the entrance and the exist edge of the last gantry magnet the parallel scanning mode is achieved. Advantageously, the resulting gantry configuration is a single-plane isocentric gantry with upstream location of a two direction magnet scanning system.
In a preferred embodiment of the present invention the ions of said ion beam are one of the group helium, carbon or oxygen ions. These carbon ions are very effective in treating patients with cancer disease. Since they have favourable physical and biological properties which can be exploited for developing improved treatment techniques in comparison to conventional proton beams, ion beams of carbon offer a unique combination of several advantages, firstly high physical selectivity, secondly higher biological effectiveness, third possibility of the irradiation verification with the aid of positron emission tomography. In the case of ions heavier than protons the favourable physical selectivity is enhanced additionally by a higher biological effectiveness which is an important advantage for the treatment of proton resistant tumours. By the proper selection of the ions species like carbon, the biological effectiveness can be controlled in such a way, that it remains low in the plateau region of the bragg curve and is elevated in the bragg-peak region. This enhances the peak to plateau ratio in terms of biological dose and enables to deliver a higher biological dose to the tumour while minimizing the dose to surrounding healthy tissue. The drawback of a proton beam is that it has only physical selectivity effect. While the radiation with high physical selectivity and additionally higher biological effectiveness is represented by carbon ions as a typical preferred embodiment.
Another preferred embodiment of the present invention has a gantry which further carries a positron emission tomography camera oriented towards an in-beam position. When the beam penetrates through the tissue, positron emitting isotops are generated by nuclear fragmentation of the primary ions. Some of these positron emitting fragments which differ from the primary particles just by the loss of one ore two neutrons (e.g. 11C, 10C in the case of carbon ion beam) stop nearly in the same region as the primary particles. The stopping point of a positron emitter can be identified with the aid of positron emission tomography. With this preferred embodiment the positron emission tomography can be applied even during the irradiation. In this preferred embodiment the localisation can be advantageously monitored in-situ and the correctness of the irradiation procedure can be verified without an additional exposure to radiation.
In a further preferred embodiment the accelerator system comprises a linear accelerator most preferably a radiofrequency quadrupole (RFQ) and an interdigital H-type structure linear accelerator and a synchrotron accelerator. The advantages of this combination of accelerators are well known for an application to treat cancer with an ion beam. This compact and cost efficient RFQ/IH combination is provided for the first time in the present invention.
In a further embodiment said ion beam therapy system comprises means of monitoring the raster scanned beam after passing the last bending magnet. With this monitor system a precise measurement and a controlling of particle fluence and of beam position is possible with a high speed within the gantry area. The last bending magnet of the gantry is preferably a bending magnet for a bending angle of more than 60xc2x0.
Preferably, the monitoring means are mounted in-beam to a common support at the gantry exit.
In a further preferred embodiment said monitoring means comprise parallel-plate-ionisation chambers and multi-wire proportional chambers. This has the advantages that the particle fluence is measured by the parallel-plate-ionisotian chambers and the beam position and width of the beam is measured by multi-wire proportional chambers wherein the whole system can consist of three parallel plate ionisation chambers and two multi-wire proportional chambers. Two of these parallel plate ionisation chambers are used to monitor the particle fluence and the two multi-wire proportional chambers determines the beam position. The third ionisation chamber is advantageously independent and serves as an diverse safety device.